1. Field of the Invention
The present invention generally relates to a method for supporting mobility of a terminal in a wireless private branch exchange. More particularly, the present invention relates to a method and system for supporting mobility of a mobile terminal in which the mobile terminal is allocated a new IP address suitable for a prefix of a sub-network after movement when moving out of an area of one sub-network into a new sub-network so that route optimization is implemented.
2. Description of the Related Art
Generally, widely used information terminals, such as a personal computer, a notebook computer, a PDA (Personal Digital Assistant) terminal, and the like, build a network called LAN (Local Area Network) to share information between them. The network can be classified into a wired LAN that is built by directly connecting information terminals using a communication cable, and a wireless LAN using access points.
In a wireless local area network (WLAN), data transmission and reception, namely, communication, is performed using radio wave or light, resulting in easy expansion and maintenance as well as free movement.
Meanwhile, by virtue of rapid development of Voice Over Internet Protocol (VoIP) technology in which transmission and reception of voice and data is performed over an IP network, an IP based communication network is substituted for a voice communication network in an enterprise and between branch offices of the enterprise. By building the voice communication network on an IP basis, it has advantages that cost consumed to build a network is saved, maintenance of the network is easily made and any other additional services can be easily built.
An IP-PBX, by which IP based networks are substituted for all existing Private Branch Exchanges (PBXs) based in-plant telephone networks, is an example in which such voice and data integration technology is applied to an in-plant telephone system. If the IP-PBX is used, IP-Phones supporting a VoIP function are substituted for all in-plant telephones, and a VoIP gateway is disposed at an interface between an enterprise and an external public switched telephone network (PSTN) to relay a transmitted and received call to the external PSTN. Further, an international telephone call or a long-distance telephone call between a head office and a branch office is linked via an external Internet, thereby saving communication cost.
However, the IP-PBX system may be advantageous in aspects of installation and maintenance of an in-plant telephone network and communication cost, but it does not provide any other conveniences for users, as compared to an existing PBX in-plant telephone system based on a circuit switching system.
Thus, a combination of wireless LAN technology and IP-PBX technology yields a system in which an IP based communication network is internally built and a public network is used at the exterior.
The increasing variety of wireless devices offering IP connectivity, such as PDAs, handhelds, and digital cellular phones, is beginning to change how the Internet is used and how these wireless devices access the Internet.
These wireless devices are convenient due to there mobility, thus it has become increasingly desired to be able to access the Internet from an area away from one's home network. Accordingly, mobile IP technology has been developed to solve this problem
The following references discussing mobile IP are incorporated by reference herein:
U.S. Pat. No. 6,147,986 to Milo Orsic and entitled “Address Updating Of Wireless Mobile Terminal Hosts Affiliated With A Wired Network” discusses assigning an address to a mobile node affiliated with a wired communications network, the address corresponding in part to a first network base station with which the mobile node becomes linked, changing the address assigned to the mobile node when the mobile node becomes linked with a second network base station, the changed address corresponding in part to an address of the second base station, and informing at least one stationary terminal host in the network of a current address assigned to the mobile node by establishing a connection between the mobile node and the stationary terminal host;
U.S. Pat. No. 6,332,077 to Chi-Kai Wu et al. and entitled “Intelligent Roaming In AGV Application” discusses a roaming algorithm for associating a mobile node with an access point (AP) in a wireless LAN system used in an automatic guidance vehicle (AGV) application. Fast roaming is achieved by eliminating a mobile node's scanning time during the search of the next AP to associate with. To eliminate the scanning time, each AP is pre-configured with its adjacent APs in advance. Whenever an AP is associated with a mobile node, the mobile node gets the information of neighboring APs from the currently associated AP. Then, the mobile node continuously monitors the signal strength of APs in its neighborhood. During roaming, the mobile node chooses the best AP to associate with without having to scan all the Aps;
U.S. Pat. No. 6,374,108 to Ken Jakobsen et al. and entitled “Assigning An IP Address To A Mobile Station While Roaming” discusses assigning a new IP address to a mobile node when the mobile node moves into a new cell (sub-network);
U.S. Pat. No. 6,490,259 to Prathima Agrawai et al. and entitled “Active Link Layer And Intra-Domain Mobility For IP Networks” discusses the use of active packets are utilized by a mobile node in a wireless network to manage the micro-mobility which includes both link layer mobility and intra-domain mobility of a wireless connection as the mobile node moves from one cell (sub-network) to another in a domain of a network. Active packets convey instructions and data so nodes in the domain may update forwarding tables maintained by each of the devices in the domain. The forwarding table entries contain both link layer entries and network layer entries to efficiently handle roaming by the mobile node. Also discussed is the assigning of a new IP address by a foreign agent (router) or dynamic host configuration protocol (DHCP) server; and
U.S. Pat. No. 6,768,726 to Jheroen P. Dorenbosch et al. and entitled “Method And Apparatus For Effecting A Seamless Handoff Between IP Connections” discusses a method and apparatus for effecting a handoff from a first Internet Protocol (IP) connection to a second IP connection using the first IP connection and a first IP address for the first station, the gateway relaying the packet data communication with a second station; setting up the second IP connection with a second IP address for the first station, the first IP connection being a primary connection and the second IP connection being a secondary connection between the first station and the gateway, the first and the second IP connection existing concurrently; determining that the second IP connection should be the primary connection between the first station and the gateway; and changing the second IP connection to the primary connection by informing the gateway that the second IP address is the primary address using stream control transmission protocol (SCTP) messages, wherein the packet data communication is immediately switched over to the second IP connection.